1. Field of the Invention
The present invention relates to an electric power steering apparatus. More particularly, the present invention relates to an electric power steering apparatus in which, when a driver abruptly operates the steering wheel, when the driver causes the steering wheel to collide with left and right lock ends at a rapid speed, or when strong impact is transmitted, which is reversely input from a road surface, the tension of a belt is increased to prevent the occurrence of a tooth jump phenomenon that causes teeth formed on the motor pulley, the nut pulley, and the belt to be jumped, and in which a tension adjusting member is slid without the operation of a motor or an operator to increase the engagement areas between the motor pulley and the nut pulley and the belt, and as a result, the noise and vibration, and the damage of the belt, which are caused as the teeth of the belt move over the teeth of the motor pulley, are prevented, and the path length of the belt is increased to increase the tension thereof.
2. Description of the Prior Art
FIG. 1 is a view illustrating a configuration of a conventional electric power steering apparatus according to the prior art. FIG. 2 is a side view illustrating a motor pulley housing and a rack housing according to the prior art.
As illustrated in FIG. 1, the conventional electric power steering apparatus includes a steering system 100 that is continued from a steering wheel 101 to opposite vehicle wheels 108, and an auxiliary power mechanism 120 configured to provide a steering assist power to the steering system 100.
The steering system 100 includes a steering shaft 102 that is connected, at one side, to the steering wheel 101 to be rotated with the steering wheel 101, and connected, at the other side, to a pinion shaft 104 via a pair of universal joints 103. In addition, the pinion shaft 104 is connected to a rack bar 109 through a rack and pinion mechanism 105, and the opposite ends of the rack bar 109 is connected to vehicle wheels 108 through tie rods 106 and knuckle arms 107.
The rack and pinion mechanism 105 is formed by a pinion gear 111 formed on a pinion shaft 104 and a rack gear 112 formed on one side of the outer peripheral surface of the rack bar 109, in which the pinion gear 111 and the rack bar 109 are engaged with each other. Thus, when a driver operates the steering wheel 101, a torque is generated in the steering system 100, and the vehicle wheels 108 are steered by the generated torque via the rack and pinion mechanism 105 and the tie rods 106.
The auxiliary power mechanism 120 includes: a torque sensor 121 configured to sense a torque that is applied to the steering wheel 101 by the driver and to output an electric signal that is proportional to the sensed torque; an Electronic Control Unit (ECU) 123 configured to generate a control signal based on the electric signal sent from the torque sensor 121; a motor 130 configured to generate an auxiliary power based on the control signal sent from the electronic control unit 123; and a belt-type transmission 140 configured to transmit the auxiliary power generated from the motor 130 to the rack bar 109 via a belt.
Accordingly, the electric power steering apparatus is configured such that a torque generated by the rotation of the steering wheel 101 is transmitted to the rack bar 109 via the rack and pinion mechanism 105, and the auxiliary power generated by the motor 130 according to the generated torque is transmitted to the rack bar 109 by the belt-type transmission 140 via a ball screw unit 150. That is, the torque generated by the steering system 100 and the auxiliary power generated by the motor 130 are combined with each other so as to cause the rack bar 109 to move in an axial direction.
In addition, as illustrated in FIG. 2, the motor 130 is fixed by coupling a gear housing 235 enclosing the motor 130 and a rack housing 207 by bolts 209. At the time of steering, when a motor shaft 203 is rotated to drive a belt 143, thereby rotating a ball nut 205 area, a force acts in a direction of pulling the motor shaft 203 and the shaft of the rack bar 109 that is provided with the ball nut 205 to each other by the tension of the belt 143.
The force generated as described above is concentrated to the bolts 209 coupling areas between the gear housing 235 and the rack housing 207 that are the mechanically weakest portions, and due to the bolt 209 releasing phenomenon by the vibration and impact generated while the motor shaft 203 is rotated at the time of steering, the motor shaft 203 is moved toward the rack bar 109 that is provided with the ball nut 205, thereby reducing the tension of the belt 143 such that the teeth of the belt 143 move over the teeth of the driving pulley 210. Thus, noise is generated and the belt 143 is damaged such that the steering assist power is not correctly transmitted.
The conventional electric power steering apparatus described above has a problem in that, when a driver abruptly operates the steering wheel, when the driver causes the steering wheel to collide with left and right lock ends at a rapid speed, or when a strong impact is transmitted, which is reversely input from a surface road, a tooth jump phenomenon that causes teeth formed on the motor pulley, the nut pulley, and the belt to be jumped is generated such that the steering assist power cannot be correctly transmitted.
In addition, the conventional electric power steering apparatus also has a problem in that, when the tension of the belt is reduced due to the aged endurance, the belt, the motor pulley, and the nut pulley are not stably engaged with each other and the engagement area is reduced such that the teeth of the belt move over the teeth of the driving pulley. Thus, noise and vibration are generated, and the belt is damaged.
In addition, when the tooth jump phenomenon is generated in a state where steering is abruptly performed in an emergency situation during the operation of a vehicle, a fatal problem may be caused in the driving stability of the vehicle.